Filter medium



July 2, 1963 s. w. BRIGGS 3,096,230

FILTER MEDIUM Filed June 23, 1960 FIBERS RESIN BEATER SHEET FORMIN G AND DRYING MACHIN E SHEET FIG.I

RESIN COATING PARTIAL CURING CASTOR OIL V COATING FLEATER FINAL CURING IMPREGNANT 2 I2 /IO RESlN-CASTOR on.

INVENTOR SOUTHWIC K W. BRIGGS ATTORNEY United States Patent 3,096,230 FILTER MEDIUM Southwick W. Briggs, Howard County, Md. (6420 Western Ave., Chevy Chase, Md.) Filed June 23, 1960, Ser. No. 38,278 12 Claims. (Cl. 162-137) This invention relates to a filter medium and a method of producing it.

The filter medium conforming to the present invention is primarily intended for the removal of colloidal carbon from oils. Whereas pleated paper filters have been employed in the past for the filtration of hot oil, there has always have the difficulty of removing particles of carbon under one micron in size. This difficulty has been overcome in accordance with the present invention in a manner which is not only very effective but is economical as well.

It is among the objects of the present invention to pro-. vide a filter medium comprising a paper body impregnated with a thermosetting oil-insoluble resin and having a coating comprising a thermosetting phenol formaldehyde resin. The oil-insoluble resin is preferably a melamine resin present in proportions between 1 /2% and 2% based upon the weight of the uncoated paper. The coating is preferably applied to one surface only of the paper body and penetrates to about one-third the thickness thereof. The coating preferably contains cold pressed castor oil in proportions ranging from 2% to 5% based upon the combined weight of the other materials present.

It is also among the objects of the invention to pro vide a filter medium comprising a paper body coated with a cured reaction product of a thermosetting phenol formaldehyde resin and cold pressed castor oil wherein the castor oil is present in proportions ranging from 2% to 5% based upon the combined weight of the other materials present.

The method contemplated by the present invention comprises impregnating paper fibers with from 1%% to 2% of an oil-insoluble theromsetting resin based upon the weight of the fibers, forming the impregnated fibers into a sheet, coating the sheet with a phenol formaldehyde resin, thereafter coating the sheet with from 2% to 5% of cold pressed castor oil based upon the combined weight of the other materials present, and curing the coating materials at an elevated temperature between 300 F. and 550 F. The phenol formaldehyde coating is preferably partially cured prior to the application of the castor oil and the curing is preferably effected by diathermy. The coating is preferably provided on one surface only of a sheet to penetrate to a depth of substantially one-third the thickness of the sheet.

In the drawings:

FIG. 1 is a flow diagram depicting certain of the steps in practicing the method of this invention; and

FIG. 2 is a fragmentary elevation depicting the product.

Whereas the procedure is subject to wide variation, an example of the manner in which a filter medium conforming to the present invention has been produced is as follows:

500 lbs. of paper fibers were added to about 2500 gals. of water in a beater and macerated. From 1V2% to 2% of melamine resin based upon the weight" of the paper fibers was added and beaten with the fibers to an extent less than that to produce gelatinization. This material was then formed into a sheet having a weight from 50 lbs. to 200 lbs. per 3000 sq. -ft., having a corresponding caliper variation of from 0.016 inch to 0.060 inch, and then dried. Then a coating of phenol formaldehyde resin was applied to one surface of the sheet in proportions sufficient to produce penetration to approxi- 3,096,230 Patented July 2, 1963 mately one-third the thickness of the sheet. The proportion-s of the phenol form-aldehyde may vary between 2% and 5% of the weight of the completed product, approximately 5% having produced highly satisfactory results. The phenol formaldehyde resin was then partially cured at a temperature between 300 F. and 550 F. by diathermy whereupon cold pressed castor oil in proportions of from 2% to 5% based upon the combined weight of the other materials present was sprayed over the previously coated surface of the sheet, and then by the renewed application of heat, employing temperatures between 300 F. and 550 F., again using diathermy, the final cure was effected. The sheet 10 depicted in FIG. 2 of the drawings is impregnated through approximate-1y one-third its thickness with the resin-castor oil reaction product 12and through the remaining twothirds with the melamine resin 14.

By virtue of the manner in which the cold pressed castor oil is applied and reacted with the previously applied phenol formaldehyde resin, the castor oil coating will remain on the fibers even when the medium is exposed to hot oils in use. The manner of applying the phenol formaldehyde sheet so as to penetrate only about onethird is thickness results in substantial economy. However, by increasing the phenol formaldehyde coating on the surface of the sheet that will be the discharge surface of the filter medium, an increase in mechanical strength will be realized without sacrificing the drainage characteristics of the material. The castor oil pl'asticizes the phenol formaldehyde resin and also protects the fibers against sulfonic acids which are so commonly found in diesel engine lubricating oils under operating conditions. Where there is no provision to protect fibers against sulfonic acids, paper filter media are actively attacked so that they soon become brittle and disintegrate. Whereas the action of the castor oil can not be explained with any great degree of certainty in this behalf, it is probable that the organic sulfur compounds present tend to sulfonate the castor oil so that the attack on the paper fibers will be substantially delayed.

It is quite likely that other thermosetting oil-insoluble resins could be substituted for the melamine resin, but thus far, despite its relatively high cost, the melamine resin is preferred since it can be used in small proportions and it is highly selective in combining with the fibers. These resins also function to hold the fibers in position since otherwise the water encountered in the lubricant would tend to produce matting and destroy the filtering properties required. In this behalf it is also important to note that the cold pressed castor oil is immiscible with the petroleum lubricant undergoing filtration and thus presents absorption of the lubricant by the filter medium.

It is very interesting to observe that the filter medium conforming to the present invention has a pore size of the order of ten times the size of the one micron carbon particles removed from the lubricant. This is probably explained as an electrochemical phenomenon. The use of cotton linters as the fiber-s has produced highly desirable results for the purposes contemplated herein. The cold pressed castor oil helps preserve the flexibility of the impregnated paper and vastly improves the efficiency of the material as a filter. Moreover, the cold pressed castor oil is both relatively stable at the high temperatures encountered in the filtration of hot oil and it remains in position on the fibers. The castor oil can not be incorporated in the resin prior to the coating operation since the mixture would become gummy and impossible to apply. Neither hydrogenated nor oxidized castor oil can be substituted since they are carried away by the hot oil.

As previously indicated, there are many possible variations of the present invention as will be suggested to those skilled in the art and which are contemplated as falling within the scope of the appended claims.

I claim: I

1. A filter medium comprising a porous paper body composed of fibers admixed with a thermosetting oilinsoluble melamine resin and having a coating comprising a thermosetting phenol formaldehyde resin penetrating through a portion only of the thickness of said body.

2. A filter medium according to claim 1 wherein said melamine resin is present in proportions between 1 /2% and 2% based upon the weight of the uncoated paper.

3. A filter medium comprising a porous paper body composed of fibers admixed with a thermosetting oilinsoluble melamine resin and having a coating on one surface only comprising a thermosetting phenol formaldehyde resin.

4. A filter medium according to claim 3 wherein said coating occupies substantially one-third the thickness of said body.

5. A filter medium according to claim 3 wherein said coating contains a reaction product of said phenol formaldhyde resin and cold pressed castor oil.

6. A filter medium according to claim 5 wherein said melamine resin is present in proportions of between 1 /2% and 2% based upon the weight of the uncoated paper and said cold pressed castor oil is present is proportions ranging from- 2% to 5% based upon the combined weight of the other materials present.

7. A filter medium comprising a paper body coated with a cured reaction product of a thermosetting phenol formaldehyde resin and cold pressed castor oil wherein said cold pressed castor oil is present in proportions ranging from 2% to 5% based upon the combined weight of the other materials present.

8. A method of making a filter medium comprising impregnating paper fibers with from l /2% to 2% of an oil-insoluble thermosetting resin, based upon the Weight of said fibers, forming the impregnated fibers into a sheet, coating said sheet with a phenol formaldehyde resin and partially curing the same, thereafter coating said sheet with from 2% to 5% of cold pressed castor oil, based upon the combined weight of the other materials present, and finally curing said coating materials at an elevated temperature.

9. A method according to claim 8 wherein said phenol formaldehyde coating is app-lied to only one surface of said sheet.

10. A method according to claim 8 wherein said phenol formaldehyde coating is applied to a depth of substantially one-third the thickness of said sheet.

11. A method according to claim 8 wherein said temperature is between 300 F. and 550 F.

12. A method according to claim 8 wherein said coating materials are cured by diathermy.

References Cited in the file of this patent UNITED STATES PATENTS 2,317,487 Schuelke Apr. 27, 1943 2,343,429 Wells et al. Mar. 7, 1944 2,566,897 Wilson et al Aug. 14, 1951 2,683,400 Denton July 13, 1954 2,802,405 Krogel Aug. 13, 1957 2,875,899 Norton Mar. 3, 1959 

8. A METHOD OF MAKING A FILTER MEDIUM COMPRISING IMPREGNATING PAPER FIBERS WITH FROM 1 1/2% TO 2% OF AN OIL-INSOLUBLE THERMOSETTING RESIN, BASED UPON THE WEIGHT OF SAID FIBERS, FORMING THE IMPREGNATED FIBERS INTO A SHEET, COATING SAID SHEET WITH A PHENOL FORMALDEHYDE RESIN AND PARTIALLY CURING THE SAME, THEREAFTER COATING SAID SHEET WITH FROM 2% TO 5% OF COLD PRESSED CASTOR OIL, BASED UPON THE COMBINED WEIGHT OF THE OTHER MATERIALS PRESENT, AND FINALLY CURING COATING MATERIALS AT AN ELEVEATED TEMPERATURE. 